1. Field of Technology
The present invention relates to an inkjet printer, and relates more particularly to a print head recovery method for cleaning the print head regularly or irregularly during inkjet printer operation.
2. Description of Related Art
Inkjet printers print by supplying ink stored in an ink cartridge or other ink source through an ink path to the print head, and then discharging ink droplets from nozzles in the print head onto the recording paper.
In order to prevent problems caused by the viscosity of ink remaining in the nozzles of the print head rising or air bubbles getting into the ink path from the nozzles, inkjet printers regularly vacuum ink from the nozzles of the print head in order to keep the print head in good printing condition.
Paper chaff and ink can also easily adhere to the nozzle face of the print head because the print head nozzle face is separated from the paper surface by a very small gap. When foreign matter such as paper chaff or ink sticks to the nozzle face, printing problems such as nozzle clogging or ink on the nozzle face soiling the paper can occur. Inkjet printers therefore also regularly clean the head to keep the print head in good printing condition by wiping the nozzle face with a sponge or other flexible absorption member to remove any foreign matter.
These ink vacuum and contaminant wiping processes are used to restore the print head to keep the print head in good printing condition, and are commonly referred to as print head recovery or restoration or print head cleaning operations. Print head recovery methods (simply “recovery process” below) are generally executed regularly every time a predetermined time has passed. The recovery process may also be executed irregularly depending upon how much time has passed and the print frequency.
Whether the recovery process is executed regularly or irregularly, the timing for executing the recovery process may come while printing is in progress. If this happens either the recovery process is delayed until after the printing process is completed, or the printing process is interrupted and the recovery process is executed first, but this can disrupt work in progress and is therefore a problem. If an inkjet printer is used as the receipt printer in the POS system of a convenience store, for example, the time for executing the recovery process could come while processing a customer purchase transaction. Giving precedence to the recovery process over the transaction process in this case is obviously undesirable because processing the customer transaction will be forced to wait. On the other hand, giving priority to customer transaction processing is also undesirable because print quality drops as a result of printing the receipt even it is time to execute the recovery process.
Japanese Unexamined Patent Appl. Pub. 2000-085150 teaches a method of addressing these problems by executing the recovery process before the deadline for the recovery process comes in order to prevent the recovery process execution time from arriving while printing is in progress.
The method taught in Japanese Unexamined Patent Appl. Pub. 2000-085150 executes the recovery process a certain amount of time before the deadline for executing the next recovery process comes after the previous recovery process ends. More specifically, the recovery process can be executed any time after a specified time that is before the time at which the next recovery process is required, but the recovery process starts only after first confirming that a printing process has not executed for a predetermined time.
Transaction processes in a supermarket, convenience store, or other retail establishment are executed suddenly and on-demand when a customer is present. A transaction process may therefore be suddenly required after the recovery process has started. Even the method taught in Japanese Unexamined Patent Appl. Pub. 2000-085150 cannot avoid demand for a printing process arising while a recovery process is in progress. More particularly, this method simply sets a predetermined time for executing the recovery process sooner than required, and the time when the recovery process starts could coincidentally come during a busy time. In this situation the likelihood of a transaction process calling a printing process while the recovery process is executing is particularly high.
The preferred time for executing the recovery process varies greatly according to the working environment of the store or business where the inkjet printer is used. This is demonstrated by the great difference in the business hours of a typical supermarket and 24-hour convenience stores, for example. The peak business hours also differ between convenience stores located in shopping areas and convenience stores in residential areas. It will thus be obvious that the best time to execute the print head recovery process depends on the type of business, the store location and environment, the region, the country, and even purchasing habits, and the best time to run the recovery process is therefore preferably set with consideration for these various conditions.